Fix service network regression on API < 1.25

[rycus86]

Hi,

A user has reported to me that my change (b2d08e6#diff-627477fe9d783a0f4c5f8627948efbb1) has broken service network create/update on Docker version 1.12.

I'm now exploring Docker versions between 1.12.6 and 17.09.0. When I ported my code from 17.09.0 to 1.12.6 for compatibility test, I found probably a python SDK issue made my swarm service unexpectedly created. The service didn't attach to the specified network but to the default one 'ingress'.

Looked at the code, probably the git commit as below introduced this issue. In this commit on source file docker/models/services.py, the argument "networks" removed from the array of "CREATE_SERVICE_KWARGS". I manually added it then the issue gone.

BTW, the APIClient() call "create_service()" doesn't have such issue. and also it works well with docker 17.xx.

Below API level 1.25 Networks was specified on the Spec, not on the TaskTemplate.

This change moves the Network back to Spec before invoking the service create/update endpoints.

Thanks!

[shin-]

LGTM, thank you!